1. Field
The present invention relates to communications. More particularly, the present invention relates to a novel and improved communication system wherein the user transmits data using code division multiple access communication channels which are transmitted in varying frequency bands and varying code channels.
2. Background
The present invention is concerned with transmitting data at rates which are higher than the capacity of a single code division multiple access (CDMA) channel.
Many solutions to this problem have been proposed. One such solution is to allocate multiple CDMA code channels to the users and allow those users to transmit data in parallel on the plurality of code channels available to them. Two methods for providing multiple CDMA channels for use by a single user are described in copending U.S. patent application Ser. No. 08/431,180, entitled “METHOD AND APPARATUS FOR PROVIDING VARIABLE RATE DATA IN A COMMUNICATIONS SYSTEM USING STATISTICAL MULTIPLEXING”, filed Apr. 28, 1997 and U.S. Pat. No. 5,777,990 entitled “METHOD AND APPARATUS FOR PROVIDING VARIABLE RATE DATA IN A COMMUNICATIONS SYSTEM USING NON-ORTHOGONAL OVERFLOW CHANNELS”, issued Jul. 7, 1998, both of which are assigned to the assignee of the present invention and are incorporated by reference herein. In addition, frequency diversity can be obtained by transmitting data over multiple spread spectrum channels that are separated from one another in frequency. A method and apparatus for redundantly transmitting data over multiple CDMA channels is described in U.S. Pat. No. 5,166,951, entitled “HIGH CAPACITY SPREAD SPECTRUM CHANNEL”, which is incorporated by reference herein.
CDMA modulation provides one means for establishing communication between users in a large system which includes a number of such users. Other techniques, such as time division multiple access (TDMA), frequency division multiple access (FDMA) and AM modulation schemes (such as amplitude companded single sideband (ACSSB)) are known in the art. However, the spread spectrum modulation technique of CDMA has significant advantages over these modulation techniques for multiple access communication systems. The use of CDMA techniques in a multiple access communication system is disclosed in U.S. Pat. No. 4,901,307, entitled “SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS”, assigned to the assignee of the present invention and incorporated by reference herein. The use of CDMA techniques in a multiple access communication system is further disclosed in U.S. Pat. No. 5,103,459, entitled “SYSTEM AND METHOD FOR GENERATING SIGNAL WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM”, assigned to the assignee of the present invention and incorporated by reference herein.
CDMA by its inherent nature of being a wideband signal offers a form of frequency diversity by spreading the signal energy over a wide bandwidth. Therefore, frequency selective fading affects only a small part of the CDMA signal bandwidth. Space or path diversity is obtained by providing multiple signal paths through simultaneous links from a mobile user through two or more cell-sites. Furthermore, path diversity may be obtained by exploiting the multipath environment through spread spectrum processing by allowing a signal arriving with different propagation delays to be received and processed separately. Examples of the utilization of path diversity are illustrated in copending U.S. Pat. No. 5,101,501 entitled “SOFT HANDOFF IN A CDMA CELLULAR TELEPHONE SYSTEM”, and U.S. Pat. No. 5,109,390 entitled “DIVERSITY RECEIVER IN A CDMA CELLULAR TELEPHONE SYSTEM”, both assigned to the assignee of the present invention and incorporated by reference herein.